Good News : Might just be your CMOS battey
Bad News: Might be board level failure
Basically, if you don't feel confident in your abilities to fiddle around and take proper ESD precautions, then just cart it off to an Acer authorised service centre.
If on the other hand, you want to have a go at replacing the battery, then Google is your friend because I'm not going to be responsible for reproducing some duff instructions. I'm not familiar with that unit.
Try Google for "Acer 5920 cmos replace".